#3 - Every time you see a gun that's a better colour than yours, you have to swap yours for it. (For example, if you have a Green AR and you see a Blue Pistol, you have to drop the AR for the pistol.) You can only have one gun at any given time but you can fill the other 4 slots with anything else because Consumables and Throwables don't count for the challenge. Lastly, if you see a gun that's the same colour as yours, it's up to you whether or not you swap it.